Mechanisms for homogeneous and heterogeneous formation of methane during the carbon–hydrogen reaction over zigzag edge sites (original) (raw)
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Physchem, 2021
The article illustrates the synergy between theoretical/computational advances and advanced experimental achievements to pursue green chemistry and circular economy technological implementations. The specific green chemistry focus concerns the production of carbon neutral fuels by converting waste carbon dioxide into methane. Both theoretical-computational and technological means were adopted to design a functional option implementing a heterogeneous catalysis process (Paul Sabatier (PS) catalytic reduction) to convert carbon dioxide into methane, and to further drive its evolution towards the employment of an alternative homogeneous gas phase plasma assisted technology. The details of both the theoretical and the experimental components of the study are presented and discussed. Future potential developments, including industrial ones, are outlined that are also from innovative collaborative economic prosumer model perspectives.
Dynamics of Catalytic Methane Coupling †
Industrial & Engineering Chemistry Research, 1997
Transient experiments at 750°C and 1 atm with methane and O 2 over Li 2 O/MgO and CeO/ Li 2 O/MgO catalysts demonstrate that coupling can occur in the absence of gas-phase oxygen. Cerium oxides increase the amount of oxygen available for the reaction. CO 2 also forms from oxygen associated with the catalyst and appears to react on the surface to produce a carbonate. Oxygen in the gas phase is needed to decompose this carbonate at 750°C. Adsorbed oxygen leads mainly to methane combustion, while most of the oxygen from the catalyst structure results in C 2 products. IE9606045 X Abstract published in Advance ACS Abstracts, June 15, 1997.
Theoretical rate constant of methane oxidation from the conventional transition-state theory
Journal of molecular modeling, 2018
The potential energy surface for the first step of the methane oxidation CH + O➔CH + HO was studied using the London-Eyring-Polanyi-Sato equation (LEPS) and the conventional transition-state theory (CTST). The calculated activation energy and rate constant values were in good agreement with the experimental and theoretical values reported in the literature using the shock tube technique and coupled cluster method respectively. The rate equation from CTST, although simple, provides good results to study the H-shift between methane and the oxygen molecules.
Thermodynamic analysis of methane synthesis by hydrogenation of carbon dioxide
WJARR, 2024
In this study, a thermodynamic analysis of methane synthesis by hydrogenation of carbon dioxide was performed. Although the standard Gibbs potential of this reaction, known as the Sabatier reaction, is negative, methane synthesis under standard conditions does not occur due to kinetic limitations. To overcome these kinetic limitations, a significant increase in temperature and pressure is necessary along with a catalyst additive. Therefore, further thermodynamic analysis of the Sabatier reaction was carried out for the real conditions of this reaction, temperature Tr = 673.15 K and pressure Pr = 3 MPa. The calculations showed that under real conditions the Sabatier reaction has exothermic enthalpy ΔrH =-181.5 kJ/ mol, and negative Gibbs potential ΔrG =-79.0 kJ/mol. Thus, methane synthesis reaction from carbon dioxide and hydrogen at elevated temperature Tr and pressure Pr is energetically and thermodynamically favorable. In addition, the equilibrium constant of this reaction Keq is 1.35 x 10 3. This value of
Thermodynamic Study: C-H Bond Activation of Methane with OsO⁺
Acta Physica Polonica A, 2015
Catalysis plays a critical role in the accomplishment of industrially significant chemical transformations, by requiring less energy investment in underlying processes. Computational chemistry has had a pronounced impact on the understanding of the role of catalysts at the atomic and molecular level, contributing to design of more efficient catalysts. In this study, we compute thermochemical properties attending C-H bond activation of methane by OsO + and enabling subsequent dehydrogenation and dehydration reactions. It is found that the dehydrogenation channel is thermodynamically more favorable. This study should contribute to the understanding of C-H bond activation using homogeneous catalysis of partial oxidation of natural gas (methane) leading to formation of the easily transported liquid fuel methanol.
Molecular and Temperature Aspects in Catalytic Partial Oxidation of Methane
Journal of Catalysis, 2000
Heterogeneous stoichiometric oxidation and catalytic partial oxidation (CPO) of methane are studied at the surfaces of MgO, α-Al 2 O 3 , and CeO 2 containing small Rh clusters. Stoichiometric reactions are linked to a repeating loop that has produced the CPO of methane at temperatures lower than 773 K with selectivity close to 100%. These reactions occur through the formation and the thermal decomposition of hydridocarbonyl Rh clusters. Molecular aspects of stoichiometric reactions are compared with those produced under stationary conditions with flows of premixed CH 4 and O 2 at very short residence time. Comparisons show that collisions between hydridocarbonyl clusters and gaseous O 2 produce CO 2 and H 2 O. IR thermography maps collected during short residence time CPO and gaseous temperature measurements are also reported. They show the existence of nonlocal thermal equilibrium between the solid and gaseous phases.
AIChE Journal, 2014
The number of active sites on the surface of carbon catalysts is an important factor in determining their activity in the decomposition of methane. Although several studies have been performed to identify the nature of these sites, no method has been established to estimate their number. A method is presented to estimate this value, and its effect on hydrogen production is evaluated, along with that of temperature and residence time. For this purpose, the thermocatalytic decomposition of methane is modeled with the inclusion of the number of active sites of the catalyst in the kinetics. The results of the model indicate the high influence of variations of small residence times in this process, and the reduction of this effect at high temperatures. Also, the effect of the number of surface sites is shown to be more prominent at low residence times and temperatures.
Density-functional calculation of methane adsorption on graphite (0001
Physical Review B, 2006
Methane adsorbed on graphite was studied using density-functional theory. The structure was fully optimized with strict energy and force convergence criteria. The methane converged to the preferred adsorption sites giving the vibrational frequencies, the energy of adsorption, charge distributions, and the electronic density of states. Under the two coverages studied ͑ ͱ 3 ϫ ͱ 3 and 2 ͱ 3 ϫ 2 ͱ 3͒ and a differing number of graphite layers ͑1-6͒, the methane molecules favored atop sites on the graphite surface with the hydrogen tripod down. We found the methane carbon 3.21 Å above the graphite carbon and the adsorption energy to be 118 meV for the lower coverage. The independent harmonic oscillator vibrational frequency perpendicular to the surface for the CH 4 molecule was computed to be 87 cm -1 . The graphite surface contracted 5.0% and 4.1% for the first and second layers, respectively, from the spacing relative to their bulk values. To benchmark our frequency calculations, we also used second-order Moller-Plesset theory and the local spin density approximation ͑LSDA͒ in GAUSSIAN 03 for the molecule. All of our LDA results are in good agreement with corresponding experiments, while under the generalized gradient approximation approximation we get only qualitatively results.